1. Field of the invention
The present invention relates to a motor drive apparatus for a brushless motor used to drive disk drive units wherein disk media such as optical disks and magneto optical disks are rotated for use and, more particularly, to a motor drive apparatus for stopping a DC brushless motor promptly to prevent reckless spinning in the reverse direction.
2. Description of the prior art
Recently, DC brushless motors wherein conductive phases are switched in due order by semi-conductors such as transistors in accordance with the output from a rotor position detector, for example comprised of hall effect devices, are widely used in the disk drive wherein disk media such as optical disks and magneto-optical disks are rotated.
With this type of disk drive, the rotation of a disk media must be reduced to a remarkably low speed, for example 30 rpm, or stopped completely so that the user can remove the disk media therefrom to replace it with another one. If not, the disk media may be damaged by any part of the disk drive during the removing operation by the user. Because it is necessary to reduce the period the user must wait for the disk drive to be ready for removing the disk media therein, a brake circuit for providing a torque command (FIG. 2) to the brushless motor to rotate in the reverse direction is required to brake the brushless motor. For this purpose, when the conventional DC brushless motor is used, the motor drive apparatus provides a reverse rotation torque command having a predetermined voltage to the motor for a predetermined period so that the motor spindle can stop completely.
However, fluctuating factors such as the size of media disks 8 cm or 12 cm in diameter for example, a motor torque, an electrical voltage in integrated circuits, temperature and humidity ambient to the disk drive may cause the time necessary for stopping the disk media to vary. Therefore, the user may access the disk media while the disk motor is still rotating. In this case, the disk media being in rotation may hit on a portion of the disk drive, and be damaged thereby. As the worse the case, the motor rotates in the reverse direction in a reckless manner.